The hydrocarbon feedstocks, the raw materials used in petroleum refining industrial industry, need to be refined before they can be used in numerous products and processes. A large part of the hydrocarbon feedstocks are submitted to a so called hydrotreating process. The purpose of hydrotreating is to reduce the amounts of impurities in the hydrocarbon feedstocks.
In particular, hydrotreating aims the removal of sulfur and nitrogen compounds.
The hydrocarbon feedstocks often contain sulfur and nitrogen compounds. These compounds are responsible of the release of sulfur oxides and nitrogen oxides in the atmosphere when the hydrocarbon products are used as fuel and burnt. These sulfur oxides and nitrogen oxides are considered harmful for the environment. As a consequence, national and international regulators are continuously imposing lower nitrogen and sulfur contents in fuel so as to reduce pollution of the environment by reducing as much as possible the quantities of these compounds when the fuel is burnt. There is thus an increased need to develop more efficient hydrotreating processes.
The efficiency of hydrotreating process relies in part on the activity of hydrotreating catalysts used. These catalysts allow converting feedstocks into useable materials. Nevertheless, at each use, the activity of the catalysts decreases. The resulting spent catalysts may thus be used in less demanding kinds of hydrotreating processes or have to be at least regenerated.
However, the regenerated catalysts do not show as high activity as the original catalysts due to the formation of agglomerates of catalyst metals.
Numerous processes have been developed in order to reactivate the spent hydrotreating catalysts such as for example the so-called rejuvenation process. The rejuvenation aims to restore the original activity of the hydrotreating catalysts or at least an activity superior to the one obtained after a simple regeneration step.
For example, document WO2005/035691 describes a process for activating a hydrotreating catalyst comprising a group VIB hydrogenation metal oxide and a group VIII hydrogenation metal oxide. This process comprises a step of impregnation with a solution comprising an acid and an organic additive which has a boiling point in the range of 80° C. to 500° C. and a solubility of at least 5 g/L (20° C., atmospheric pressure). After the impregnation step, the catalyst is then dried to maintain at least 50 wt % of the additive after drying.
However, the efficiency of the rejuvenation process may depend on several parameters such as: the catalyst to be treated, the operational conditions of the process or the rejuvenating agent used.
Thus, there is still a need to develop efficient and easy to implement processes for restoring the activity of the spent hydrotreating catalysts.